758 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



Calverf critically reviewed and correctly stated the matter, adding J 

 some results of his own. I have been al)le to extend the study of 

 homologies in a few parts, such as the region of the bridge, the sup- 

 plements, the anal area, and several spaces in which special bracings 

 occur. In these places occur the most distinctive venational features 

 of the smaller groups. 



{(•) Incidentally, I have shown something of the relative values of 

 the different characters that have been used hitherto to distinguish 

 groups. Characters drawn from the form and position of the arculus . 

 and triangle and other strong braces have always proved reliable, but l| 

 it is very clear that antenodal and other cross veins have been greatly v. 

 overvalued, and it is equally clear that many other more important i, 

 venational characters have not been noted. It is not the presence or }] 

 absence of weak cross veins, but the position and relations of those that 1 

 strongly brace the wing; not the number of rows of areoles that may y 

 till a wide area, but the course of principal veins and of their sup- 

 porting sectors, that are of first importance. 



{(I) I have been able to indicate many new minor lines of special!- , 

 zation within the order, and to add new and corroborative evidence to ,1 

 some lines alreadv indicated by Kollie, Karsch, and Calvert. Owing : 

 to the presence in these wings of a number of characters which may :, 

 vary independently, for each of which primitive conditions are easily J 

 determined, and in each of which the several courses of specialization 

 are easily traced, I have often been able to put forth conclusions 

 based on the cumulative testimony of several parts. I have attempted 

 to find such genealogic evidence as is preserved — not to create any — 

 and have been content to drop, without any suggestion that might 

 hinder future studies, cases in which evidence from wings alone seemed 

 insufficient. But 1 have not hesitated to indicate relationships when 1 

 these seemed well evidenced by the facts of venation. 



4. Following my morphological stud}" of the order with a review of 

 its members, as distributed among the several families and genera, I Ij 

 mention some facts which might themselves serve independently as ; 

 biological indications of specialization: 



(a) A large group of closely related species, numerically dominant 

 in \t^ proper range, indicates the culmination of some type of speciali- 

 zation. This may affect either the nymph or the adult or both. 



{h) Small and scattered genera, which include only the more rare and 

 delicate species, are pretty apt to be the conservators of numerous 

 generalized characters. However, since development has not stood 

 still with any species, certain marks of specialization will also always- 

 appear. 



"Trans. Amer. Ent. Soc, XX, pp. 162-169. The papers therein discussetl, together' 

 with the few referred to in footnotes to these pages, constitute the whole of tiie use-' 

 ful literature of Odonate venation, hence no bibliographic list is hereto appended. 



